Schema properties allow you to describe the individual properties of the digital objects you pass back and forth as part of each API request and response, describing the name, type, shape, patterns, and depth of each object. Schema properties define what is possible with each API request and response, and should speak to what API consumers are needing across applications.
Each schema property you add will need to stay until the next major release of an API, or longer. Schema properties shouldn’t be added without thinking through the wider relationship and impact the property will have across an object, but also across all objects. Keep the properties of your objects plain language, driven by a vocabulary, and coherently organized for consumers.